The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
An engine may generate power by combusting an air and fuel mixture within cylinders of the engine. The fuel and air may be controlled such that the engine maintains an air-to-fuel ratio at stoichiometry. The engine may operate using fuels with different stoichiometric values, such as a gasoline and ethanol blend. As the percentage of each fuel in the overall fuel mixture changes, the stoichiometric value may change.
The stoichiometric value of a fuel mixture may be measured to allow for optimal operation of the engine based on the particular fuel mixture. The engine system may change the relative amounts of air and fuel delivered to the cylinders based on the stoichiometric value for the fuel mixture. In vehicles with a single fuel tank, the fuel mixture may undergo substantial change when the vehicle is refueled, as the new fuel introduced to the fuel tank may have a different fuel mixture than the fuel originally in the fuel tank. The new fuel composition may be measured by direct measurement using a hardware sensor.
The fuel mixture may also be calculated from other measured parameters and known relationships in a manner such as that described in commonly-assigned U.S. Pat. No. 7,159,623 (issued Jan. 9, 2007), the disclosure of which is incorporated herein by reference. Exhaust sensors such as oxygen sensors may measure the content of an exhaust flow from an engine. Based on measured values, the fuel and air supplied to the engine may be adjusted, i.e., trimmed, to correct for deviations from a desired air-to-fuel ratio. These fuel trim values may be stored in a memory structure such as a plurality of closed loop correction (“CLC”) cells. The stored CLC values representing fuel trim over time may be used to calculate a fuel composition.
Some vehicles have more than one fuel source. Each fuel source may have a different fuel composition. The fuel sources may intermix during vehicle operation such that the fuel mixture supplied to the engine may change multiple times during normal vehicle operation rather than upon refueling.